Even though RTW has tbs element, the core of the play is the real time battles. So if your kid likes more building and that kind of stuff, he doesn't necessarily like RTW.
I had first little motoric difficulties getting accustomed to the game, I had played only civ before it. So if your kid hasn't played anything like that before, it can be little challenging too.
The battles get harder as the game progresses, so it can be little frustrating.
And lastly, it's more centered around fighting, and it's attitude to violence might be something you wouldn't like to introduce to your kid.
Perhaps you should ask what your kid likes exactly likes in civ. Does he like more completing wonders or crushing his enemies? Or just to look the history of the world?
And also, you can download demo of it and try it out.
Here's one, I don't know if there's different versions, but googling helps.